It might be cheaper to buy one of the consumer NAS appliances such as the DLink DNS-321.
A number of the NAS appliances, including the aforementioned include RAID.
Without RAID, you can put something together around $200 depending on how much disk storage you want. With RAID 1 support and say 1 TB of storage, costs can go up to $360 to $450, sales tax included.
Just about all these units can be managed via a web interface.
Unless you want the thrill of putting a system together and configuring the OS, etc..., this will get you up faster and may cost less (for new parts anyway).
- Tom